An RFID (Radio Frequency Identification) label or tag is capable of being read and written in a non-contact manner and resistant to the influence of dirt and dust. Thus, RFID technology is continuously used as a substitute for barcode technologies.
However, there is a demand to use both barcodes and RFID tags practically in stores. To meet such a demand, a RFID tag writing system is provided which is capable of printing basic commodity data such as a commodity name, a price, and a barcode on a label and writing the basic data and other detailed data in a RFID tag embedded in the label.
In a conventional calibration carried out in a RFID writing system, the setting of electromagnetic wave transmission power of and optimal writing position for RFID labels having different features is relatively cumbersome and needs to be manually done by professionals using special tools. Thus, normal users cannot conduct the calibration.
Hence, an automatic calibration device is provided to solve the problem above. The automatic calibration device calculates an optimal writing position by conveying RFID labels by a specific feeding distance. However, the feeding of a whole label takes a long time, and the transmission power of an electromagnetic wave and a dynamic range of an AGC (Automatic Gain Control) unit at a receiving side are not taken into consideration. Thus, the following problems are encountered.
Even though an optimal writing position is calculated through the calibration, if the electromagnetic wave output from a RFID reader-writer is too powerful, the electromagnetic wave will flow through a RFID tag embedded in another label also. Consequentially, the RFID reader-writer receives a response from a plurality of RFID tags. In this case, data are not written to a target RFID tag to which data is to be written or the same information is written to a plurality of RFID tags. In addition, an optimal writing position may not be found if the intensity of the electromagnetic wave output from a RFID reader-writer is too weak. As a result, there is still a problem that optical writing parameters may not be set even if the conventional automatic calibration is carried out.
In addition, in practical use, as the same calibration values are effective for RFID labels having the same specification, in most cases, it may be unnecessary to carry out an automatic calibration.
On the other hand, there is a problem that it cannot be determined whether or not a manually-set calibration value is appropriate without writing data in the RFID tag even if the calibration value is slightly shifted from the originally-set value.